1. Field of the Invention
The present invention relates to a method and an apparatus for wireless communication network, preferably Universal Mobile Telecommunication System (UMTS), operating in compressed mode, and in particular, to the method and the apparatus for use by a user equipment that supports HSDPA, and a network node in communication with such a user equipment.
2. Description of the Related Art
High Speed Downlink Packet Access (HSDPA) is emerging as a promising candidate for providing high bit rate transmission of packetized data in third generation wireless telecommunication networks. It is expected that once implemented Wideband Code Division Multiple Access (WCDMA) networks using HSDPA will be able to provide data transmission at rates in the order of 10 Mbps.
In the HSDPA method, as a physical channel for a downlink through which data are transmitted from a base station to a mobile wireless terminal, an HS-SCCH (High Speed-Shared Control CHannel) and an HS-PDSCH (High Speed-Physical Downlink Shared CHannel) are additionally provided. The HS-SCCH is used to transmit control information of the HS-PDSCH pairing up with the HS-SCCH, while the HS-PDSCH is used to transmit packet data employed in the HSDPA method. Moreover, the HS-PDSCH can use a maximum 15 pieces of channelization codes in units of subframes, which is called a multi-code, and the number of used multicodes is called the multicode number. The subframe denotes a frame length of a physical channel used in the HSDPA method expressed in time units of three slots and a slot denotes a time unit designated by the 3GPP.
The implementation of HSDPA specified by the 3rd Generation Partnership Project (3GPP) requires that any transmission scheme used for HSDPA is compliant with the compressed mode used by UMTS user equipments when performing inter-frequency or inter-system measurement as a preparation for a handover.
As will be known to those skilled in the art a handover is a process whereby the user equipment changes the way in which it access the radio network, for example, by changing cell or radio access mode.
In a UMTS network if a user equipment is required to perform a inter-frequency or inter-system handover, the node B (base station) instructs the user equipment to operate in the compressed mode. In compressed mode a gap is created by obeying predefined patterns in certain radio frames transmitted between the node B and user equipment, in which the node B and user equipment can perform various measurements of network parameters to prepare for the handover. For example, base stations in cells surrounding the current cell of user equipment may perform signal strength measurements for the user equipment in order to determine which of the base stations the user equipment should handoff to. In the downlink direction a transmission gap is inserted into predetermined frames on the Dedicated physical channel (DPCH).
One of the drawbacks of HSDPA is that the high data reception rate at the user equipment requires a large amount of digital signal processing to be performed in the user equipment and this processing burden has a detrimental effect on the battery life of user equipments.